1. Field of the Invention
The present invention relates to a frame assembly of a shadow mask in a flat Braun tube, and, more particularly, to a frame assembly of a shadow mask in a flat Braun tube, in which a stress on a shadow mask is reduced for minimizing creep during an elevated temperature process, and a low tension on the shadow mask is corrected effectively during operation of a flat Braun tube after the elevated temperature process, for preventing deterioration of a color purity caused by deterioration of howling and doming.
2. Background of the Related Art
FIG. 1 illustrates a side view with a partial cut away view of a related art flat Braun tube. Referring to FIG. 1, the related art flat Braun tube is provided with a flat panel 1 having three colors of red, green, and blue fluorescent film 4 of a dot type, a shadow mask 3 having a plurality of electron beam pass through holes 3c for selective pass of the incident electron beams, a funnel 2 welded to rear of the panel 1, a neck part 2a formed in a rear portion of the funnel 2, electron beams(not shown) fitted inside of the neck part 2a for emitting electron beams, a deflection yoke 5 around an outer circumference of the funnel 2 for deflecting the electron beams 6, a shadow mask frame assembly 7 for supporting the shadow mask 3, springs 8 fitted to a supporting frame, stud pins 10 coupled with the spring 8 fixed to an inside of the panel 1 for holding the shadow mask frame assembly 7, and an inner shield 9 in rear of the supporting frame 5 for shielding the electron beams 3 from an external geomagnetism in operation of the cathode ray tube for preventing the electron beams from being influenced by the geomagnetism.
Upon putting the flat Braun tube into operation, the electron beams 6 emitted from the electron gun is deflected in a horizontal, or vertical direction by a magnetism of the deflection yoke 5, directed onto the shadow mask 3, pass through the electron beam pass through hole 3c in the shadow mask 3 selectively, land on the fluorescent film 4, to form a picture.
FIG. 2 illustrates a perspective view of a shadow mask frame assembly in a related art Braun tube, and FIG. 3 illustrates a shadow mask showing a state of tension applied to the shadow mask, schematically.
Referring to FIGS. 2 and 3, the shadow mask frame assembly 7 in a related art Braun tube is provided with two main frames 7a for applying a tension P1 to the shadow mask 3 having fixed opposite ends, two sub-frames 7b perpendicular to the main frame 7a connected to one ends of the main frames 7a, and a thermal compensating plate 11 attached under the sub-frames 7b. The shadow mask 3 has an effective surface 3a having the electron beam pass through holes 3c formed therein, and an edge part 3b having no electron beam pass through holes 3c formed therein for reinforcing a rigidity of the effective surface 3a. The shadow mask frame assembly 7 is designed to have a high rigidity in a structure basis. If a preset tension P1 is provided to the shadow mask 3 by the shadow mask frame assembly 7 having such a high rigidity, a natural frequency of the shadow mask 3 becomes higher, thereby permitting to prevent howling, in which the shadow mask 3 vibrates during operation of the cathode ray tube.
In the meantime, the shadow mask 3 having the preset tension applied thereto by the shadow mask frame assembly 7 is subjected to an elevated temperature process(at approx. 470xc2x0). Due to this elevated temperature process, there is a permanent deformation occurred at the shadow mask 3 caused by creep. In the creep, if a constant load is applied to the material for a prolonged time period under a certain temperature, a strain increases as time passes by while the stress on the material is reduced. Therefore, the permanent deformation of the shadow mask caused by the creep becomes the greater as the stress on the shadow mask becomes the greater in the elevated temperature process. At the end, the creep reduces the tension on the shadow mask 3 provided by the frame 7 after the elevated temperature process in comparison to the same before the elevated temperature process, which leads to a poor howling characteristics of the shadow mask 3 during operation of the cathode ray tube, causing a poor color purity by a beam landing error of the electron beams 6. Therefore, in order to reduce the stress relaxation following deformation of the shadow mask 3 caused by the creep during the elevated temperature process, the thermal compensating plate 11 is fitted under the sub-frame 7b. FIG. 4 illustrates shadow mask assemblies for showing stresses to the shadow masks from the thermal compensating plate 11 under a room temperature and the elevated temperature, schematically. Referring to FIG. 4, the thermal compensating plate 11 is formed of a material having a thermal expansion coefficient greater than the sub-frames 7b, so that the thermal compensating plate 11 makes the sub-frames 7b to deform in a xe2x80x9cUxe2x80x9d form when the thermal compensating plate 11 is heated in the elevated temperature process. This deformation reduces the tension P1 to the shadow mask 3, to reduce the stress on the shadow mask 3, allowing to reduce the stress "sgr" on the shadow mask 3 in the elevated temperature process in comparison to the stress a on the shadow mask 3 in the room temperature, which reduces an influence of the creep and deformation caused by the creep. According to this, the tension to the shadow mask 3 can be maintained a state the most close to the tension before the elevated temperature process is carried out even after the elevated temperature process is carried out. At the end, the creep of the shadow mask 3 can be reduced by the thermal compensating plate 11, to reduce the stress relaxation caused by the shadow mask 3 after the elevated temperature process is carried out.
However, though the bimetallic action of the thermal compensating plate 11 in the related art can reduce the influence of creep in the elevated temperature process by deforming the sub-frames 7b, there is a problem in that the sub-frames 7b are deformed in the xe2x80x9cUxe2x80x9d form even when the flat Braun tube is in operation as the shadow mask 3 is heated by the electron beam 6, and the heat is transferred to the thermal compensating plate 11. As shown in FIG. 5, this deformation causes a problem of poor color purity of the picture, which deteriorates a reliability of the product, by a beam landing error of the electron beams 6 as the doming in which the shadow mask 3 moves toward the panel is occurred, and the weak tension to the shadow mask 3 deteriorates the howling characteristics.
Accordingly, the present invention is directed to a frame assembly of a shadow mask in a flat Braun tube that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a frame assembly of a shadow mask in a flat Braun tube, which can reduce a stress on the shadow mask during an elevated temperature process for minimizing an influence from creep, and compensate for tension reduction of the shadow mask effectively when the flat Braun tube is in operation after the elevated temperature process for minimizing doming, and improve howling characteristics.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the frame assembly of a shadow mask in a flat Braun tube includes a main frame fitted to the shadow mask, sub-frames connected between both ends of the main frame, and a thermal compensating plate fitted to a bottom of the sub-frames, wherein a ratio(h/t) of a height xe2x80x98hxe2x80x99 of the sub-frame to a thickness xe2x80x98txe2x80x99 of the thermal compensating plate is within a range of 4xcx9c8.
In another aspect of the present invention, there is provided a frame assembly of a shadow mask in a flat Braun tube including a main frame fitted to the shadow mask, sub-frames connected between both ends of the main frame, and a thermal compensating plate fitted to a bottom of the sub-frames, wherein a ratio(b/bxe2x80x2) of a width xe2x80x98bxe2x80x99 of the sub-frame to a width xe2x80x98bxe2x80x99 of the thermal compensating plate is within a range of 0.8xcx9c1.3.
In other aspect of the present invention, there is provided a frame assembly of a shadow mask in a flat Braun tube including a main frame fitted to the shadow mask, sub-frames connected between both ends of the main frame, and a thermal compensating plate fitted to a bottom of the sub-frames, wherein a ratio(1/1xe2x80x2) of a length xe2x80x98lxe2x80x99 of the sub-frame having the thermal compensating plate fitted thereto to a length xe2x80x98lxe2x80x2xe2x80x99 of the thermal compensating plate is within a range of 0.8xcx9c1.3.
In further aspect of the present invention, there is provided a frame assembly of a shadow mask in a flat Braun tube including a main frame fitted to the shadow mask, sub-frames connected between both ends of the main frame, and a thermal compensating plate fitted to a bottom of the sub-frames, wherein a ratio(h/t) of a height xe2x80x98hxe2x80x99 of the sub-frame to a thickness xe2x80x98txe2x80x99 of the thermal compensating plate is within a range of 4xcx9c8, a ratio(b/bxe2x80x2) of a width xe2x80x98bxe2x80x99 of the sub-frame to a width xe2x80x98bxe2x80x2xe2x80x99 of the thermal compensating plate is within a range of 0.8xcx9c1.3, and a ratio(1/1xe2x80x2) of a length xe2x80x98lxe2x80x99 of the sub-frame having the thermal compensating plate fitted thereto to a length xe2x80x98lxe2x80x2xe2x80x99 of the thermal compensating plate is within a range of 0.8xcx9c1.3.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.